Proper estimation of pore size distribution (PSD) for various solid adsorbents is essential for efficient characterization of such materials. PSD determination is inherently an ill-posed problem which can be solved by resorting to Tikhonov regularization technique. Automatic selection of the optimal regularization level is crucial for efficient extraction of PSD from experimental adsorption or condensation isotherms. A detailed comparison of Leave One Out Cross Validation, L-curve, U-curve and modified L-curve criteria are presented using several real adsorption and condensation case studies. A modified U-curve criterion is also proposed and its superior performances are thoroughly validated. The new method employs a relatively simple minimization procedure, which is much easier than quite complex and tedious procedures used by conventional methods to compute their internal optimum parameters. Other practical issues, such as efficient computation of L-comer have been received proper attention in this article and a simple algorithm is presented for this purpose. (C) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.